Lincoln Electric POWER MIG SVM157-A Service Manual page 32

E-4
FAN
MOTOR
LINE
SWITCH
RECONNECT
PANEL
TRANSFORMER
CONTROL BOARD, GUN
TRIGGER AND WIRE DRIVE
MOTOR
When the control board receives an activation
command from the trigger circuit the control
board activates the gas solenoid, output
contactor, and the wire drive motor. The control
board monitors the motor 's tach feedback
signals and compares these to the wire speed
control setting. The proper armature voltage is
then applied to the wire drive motor. The drive
motor speed is thus controlled which in turn
regulates the electrode wire feed speed through
the gun.
Two thermostats are included in the trigger
circuitry. If either of these thermostats would
"open", the trigger circuit would be interrupted
and the machine's output would be disabled.
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
THEORY OF OPERATION
FIGURE E.4 – OPTIONAL CIRCUITS.
GAS
SOLENOID
CONTROL BOARD
RECTIFIER
DIODE
BRIDGE
TAP SELECTOR
SWITCH
CONTACTOR
MAIN
POWER MIG 200
WIRE
SPEED
CONTROL
WIRE
DRIVE
MOTOR
TRANSFORMER
TACH
THERMOSTAT
FEEDBACK
GUN TRIGGER
OUTPUT DIODE
BRIDGE
+
+
OUTPUT
POSITIVE
CHOKE
TERMINAL
OUTPUT
CAPACITORS
- -
NEGATIVE
TERMINAL
E-4
OUTPUT BRIDGE
THERMOSTAT
GUN
ASSEMBLY